EP 01722267 (Samsung) describes a uniform direct-view backlight whereby a plurality of LED (light emitting diode) light sources is interspersed with vertical reflective barrier columns that extend across the horizontal width of the display. These columns support a diffusion plate that sits behind a liquid crystal display. The columns separate more than one LED in a row. Synchronous switching of the rows of LEDs between the columns with the display refresh rate allows reduced motion blur artifacts.
US 2006/0290840 (LG Philips) describes a uniform direct-view backlight whereby a regular array of LEDs is positioned on a circuit board behind a liquid crystal display (LCD). Each LED has a lens structure made into the LED to modify the emission profile. There also exist supports for an optical diverter spaced between the LEDs and the display. The optical design of the diverter and LED lens structure is such as to give a uniform illumination of the display.
U.S. Pat. No. 7,072,096 (Digital Optics International Corporation) describes a uniform direct-view backlight composed of an array of LEDs and one or more prism sheets to form a uniform directed illumination arrangement. One embodiment describes the use of vertically orientated triangular mirrors surrounding zones containing a plurality of LEDs. These mirrors recycle reflected light from the prism film and improve brightness.
WO 05071643 (Shanghai Sansi Technology Co.) describes a uniform direct-view backlight utilizing an array of LEDs placed a fixed distance behind an LCD. Each individual LED has a rounded square reflector extending vertically from the circuit board on which the LED is mounted. The reflector has a circular cross-section. The purpose of the patent is to improve brightness of the display by sending more high-angle light forward.
JP 2006/190847 (Citizen Electrical) describes a uniform direct-view backlight comprising an array of LEDs placed a fixed distance behind an LCD. Surrounding the whole array is a vertical mirror that extends from the LED plane to the LCD. The purpose of this patent is to improve colour uniformity towards the edges of the display as more light is lost from these areas.
U.S. Pat. No. 25,128,744 (Dialight Corporation) describes an LED array for directed light applications whereby one or more of the LEDs are surrounded by a circular reflector with a conic cross section. The reflectors are identical and arranged uniformly across the array. The purpose of this system is to replace lenses for illumination applications, for example in a traffic light.
FIG. 1 of the accompanying drawings illustrates a typical display of known type that is used in large area devices such as large area televisions and display screens. The display, 1, comprises a flat transmissive spatial light modulator (SLM) in the form of a liquid crystal display (LCD) panel 4 having input and output polarisers 2 and 3. The panel 1 is provided with a backlight 9, whose main components are a diffuser 5, an array 6 of small point-like light sources 11 and a rear reflector plane 7. There may also be separation pillars 8 which may be transparent and are designed to maintain the separation between the diffuser 5 and the light source plane 6.
There is also driving electronics 12 for the light sources 11. Prism based brightness enhancement films and polarised reflectors (not shown) may also be used.
The light source array 6 and diffuser 5 have an area or “size” in a plane perpendicular to the plane of FIG. 1 at least as big as the display area of the panel 4 with a thickness typically much less than its other dimensions. The backlight unit 9 is placed behind the LCD 4 and is directed to illuminate the rear part of the LCD and through to the observer 10.
The backlight unit 9 comprises the diffuser 5, which that is placed nearer to the LCD 4. Behind the diffuser 5, parallel thereto and at a fixed distance therefrom, there is placed the light source array. Each element of the array is substantially identical and emits light in a parallel direction towards the diffuser. The reflector plate 7 sits surrounding the light source array and is used to recycle reflected light back through the system to improve brightness.
The small point-like light sources 11 may be Light Emitting Diodes (LEDs).
The light source array 6 may comprise individual LED structures 11 utilising blue or ultraviolet LEDs with phosphors, or integrated red, green and blue LEDs located close to each other as a single “point” in the array. LED driving electronics 12 are typically positioned behind the reflector plate.
The action of the diffuser 5 is to spread the emitted light from the LEDs over a wide angle and to form the basis for a comfortable viewing plane for the observer 10. However, single diffusers are typically inefficient at improving the spatial uniformity of illumination passing through them. Thus it is necessary to have reasonably uniform illumination onto them from the light plane 6.